Anyway, beside the register I found another display of diecast cars. There I discovered not only a few more 1/55s but also two Hot Wheels mid scales: a Dodge Neon SRT-4 and a VW Golf Mk4 (the Spinner in the pic is actually from the BladeRunner limited edition box set, not a find at HOBBY OFF).
I got them all and brought them home to measure and scale. I must get a proper pair of calipers for this in the future, but for the time being I make do with a tape measure. I measure length, width (without mirrors), width, height, and wheelbase. Calculations put all of the five I eyeballed as 1/55s as very close:
Jada '03 Infiniti G35 coupe = 1/56
Jada '03 Dodge Magnum R/T station wagon = 1/55
Jada '02 Nissan Silvia S15 coupe = 1/51
Jada Mitsubishi Lancer Evo VIII sedan = 1/54
Realtoy MB G-Wagon 460 2-dr = 1/56
True, the Silvia (far left) is a bit big, but since it was a small car it mixes well with the others.
Hot Wheels mid-scales are sold as 1/50s. I have a number of them, mostly 60s and 70s American muscle from the G Machines line with a few modern imports from the Dropstars line. These cars are well proportioned for minis, typically 1/50 in all dimensions but width, which is exaggerated to 1/43. Perfect for the exaggerated bulk of mini sculpts. 28mm figures aren't dwarfed by the car when standing beside it, but can reasonably fit inside with appropriate shoulder room. Truly the best of both worlds.
Sadly the mid-scale range seems to have been abandoned by HW, and the cars tend to fetch premium prices due to the HW collector's community. When I seached for more SRT-4s, with the idea of using the sedans as cop cars, I found them to run for about $50. That's crazy. Still, I'll pick them up as I see them, hoping to replace the 55s in the future.